To provide a card not suffering from warpage caused by the affection of heat, and a method of preventing the warpage of cards by solving problems in which a card is bent through the occurrence of warpage by heat within a reader-writer after the insertion of the card into the reader-writer with the consequence that the card can not be removed from the reader-writer under the influence of residual stress as the card is exposed at a high temperature environment.

The card is formed such that lamination is done at a symmetrical position with respect to the obverse and reverse direction of a card from the central part of a plurality of base main bodies 8 that constitute the card base main bodies, wherein printing layers 11, 12 of designs, patterns and the like are formed on the obverse side base material of the card, and the printing layers 11, 12 are formed on a base material regional part corresponding to an obverse and reverse symmetrical position with respect to the base material with the printing layers 11, 12 formed on the reverse side of the card.